Ecological systems often exhibit resilient states that are
maintained through negative feedbacks. In ponderosa pine forests,
fire historically represented the negative feedback mechanism
that maintained ecosystem resilience; fire exclusion reduced
that resilience, predisposing the transition to an alternative
ecosystem state upon reintroduction of fire. We evaluated the
effects of reintroduced frequent wildfire in unlogged, fire-excluded,
ponderosa pine forest in the Bob Marshall Wilderness, Montana,
USA. Initial reintroduction of fire in 2003 reduced tree density
and consumed surface fuels, but also stimulated establishment
of a dense cohort of lodgepole pine, maintaining a trajectory
toward an alternative state. Resumption of a frequent fire regime
by a second fire in 2011 restored a low-density forest dominated
by large-diameter ponderosa pine by eliminating many regenerating
lodgepole pines and by continuing to remove surface fuels and
small-diameter lodgepole pine and Douglas-fir that established
during the fire suppression era. Our data demonstrate that some
unlogged, fire-excluded, ponderosa pine forests possess latent
resilience to reintroduced fire. A passive model of simply allowing
lightning-ignited fires to burn appears to be a viable approach
to restoration of such forests.